Shaping of hollow workpieces

ABSTRACT

A hollow workpiece to be ironed is subjected to a relatively large frictional force at its interior engaged by a punch, and to a smaller frictional force at its outside engaged by a die, whereby tensile stresses in the ironed portion of the workpiece are decreased and larger reductions in wall thickness are rendered possible per die. Deep drawing may be combined with ironing and both performed during a single stroke of the punch.

United States Patent 91 Avitzur Reissued Aug. 12, 1975 SHAPING OF HOLLOW WORKPIECES [76] Inventor: Betzalel Avitzur, 817 31st St.,

Allentown, Pa. 18104 [22] Filed: Aug. 8, 1974 [21] Appl. No.2 495,853

Related US. Patent Documents Reissue of:

[64] Patent No.: 3,685,337

Issued: Aug. 22, 1972 Appl. No.: 889,218 Filed: Dec. 30, 1969 [52] US. Cl. 72/347 [51] Int. Cl. B21D 22/20 [58] Field of Search 72/41, 43, 45, 347, 348, 72/349, 253, 370, 467, 468; 29/12, 1.21, 1.3

[56] References Cited UNITED STATES PATENTS 211,342 l/1879 Palmer 72/347 2,821,156 1/1958 Lyon 72/348 3,359,775 12/1967 Langewis 72/349 3,360,157 12/1967 Bolt et a1. 113/120 A 3,459,021 8/1969 Fuchs, .Ir. 72/347 FOREIGN PATENTS OR APPLICATIONS 625,011 6/ 1949 United Kingdom 72/349 807,085 6/ 1951 Germany 72/60 834,626 5/1960 United Kingdom.. 72/60 1,468,073 12/1966 France 72/60 OTHER PUBLICATIONS Promotion of Fluid Lubrication in Wire Drawing by Christopherson et al., pp. 643-653; Proc. Inst. Mech. Eng.; 169; 1955.

Primary ExaminerRichard J. Herbst Attorney, Agent, or FirmEric Michelson [5 7] ABSTRACT 18 Claims, 26 Drawing Figures 36 34V y i F -I ZONE II 3 V--F5 L 38 R ZONE III 7 ZONE I Ri Reissued Aug. 12, 1975 Re. 28,511

25 Sheets-Sheet 1 F /6. la

INVENTOR. BETZALEL AV/TZU/P fie-issued Aug.-1Z, 1915 Re. 28,511

25 Sheets-Sheet 5 INVENTOR. BETZALEL AV/TZUI? F/G. Ia BY Reisaued Aug. 12, 1975 I Re. 28,511

25 Sheets-Sheet 4.

ZONE 1 FIG. 2

INVE N T'OR. BETZALEL AV/TZUR Reissueci Aug. 12, 1973 25 Sheets-Sheet 5 an LIMITED DUE m "xb T0 WALL TENSION WEIGHTED IRONING FORCE SEMI CONE ANGLE FlG.3cl WEIGHTED IRQNING FORCE AS A FUNCTION OF a AND m IBE'IZALEL AVITZUR INVENTOR.

zwm w Reissued Au 12, 1915 25 Sheets-Sheet 6 WEIGHTED IRONING FORCE SEMI-CONE ANGLE FIG. 3b WEIGHTED IRONING FORCE AS A FUNCTION OF 0 AND m BETZALEL AVITZUR INVENTOR.

Reissued Aug. 12, 1975 25 Sheets-Sheet 7 LIMITED DUE TO WALL TENSION WEIGHTED IRONING FORCE SEMI CONE ANGLE FIG.40 WEIGHTED IRONING FORCE AS A FUNCTION OF 0 AND 1 /1,.

BETZALEL AVI TZUR INVENTOR.

L m MJW Reissued Aug. 12, 1975 WEIGHTED IRONING FORCE 25 Sheets-Sheet 8 it LIMITE D DUE TO WALL TENSION Oil SEMI CONE ANGLE FIG. 4b WEIGHTED IRONING FORCE AS FUNCTION 0F 01 AND t m.

BETZALEL AVITZUR INVENTOR.

Reissued Aug. 12, 1975 25 Sheets-Sheet 9 o m w momom 0220: QMPIOEB SEMI-CONE ANGLE FIG.5 WEIGHTED IRONING FORCE AS A FUNCTION OF 0 AND m BETZALEL nvnzun INVENTOR.

Reiasued Aug. 12, 19 75 25 Sheets-Sheet 10 l LO 20 SEMI -CONE ANGLE OF a AND m BETZALBL AVITZUR INVENTOR.

ike'issueci i9??? 25 Sheets-Sheet 11 SEMI-CONE ANGLE BETZALEL AVITZUR OF 0 AND m INVENTOR.

Reisaued Aug. 12, 1975 25 Sheets-Sheet 12 SEMI-CONE ANGLE FIG.70 RELATIVE WALL TENSION AS A FUNCTION OF 0 AND 1 /1,.

smzALBL AVITZUR INVENTOR.

; Reissued Aug. 12, 1975 Re. 28,511

25 Sheets-Sheet 13 l l G 30 4o 50 SEMI-CONE ANGLE F|G.7b RELATIVE WALL TENSION AS A FUNCTION OF a AND r /t BETZALEL AVITZUH IN VENTOR.

Reissued Aug. 12, 1975 RELATIVE WALL TENSION 25 Sheets-Sheet 14 O' L O .2 t

f EQ.(| I) O l l l l 0 IO 20 3O 4O SEMI-CONE ANGLE OF a AND m BETZALEL AVI'IZUR INVENTOR.

Reissued Aug. 12, 1975 25 Sheets-Sheet 15 SEMI-CONE ANGLE FIG.9 MAXIMUM POSSIBLE THICKNESS RATIO AS A FUNCTION 0F 0 AND m BETZALEL AVITZUR INVENTOR.

#7 1 WMMM Reiaaued Aug. 12, 1915 Re. 28,511

25 Sheets-Sheet 16 MAXIMUM POSSIBLE THICKNESS RATIO SEMI-CONE ANGLE FIG.|O MAXIMUM POSSIBLE THICKNESS RATIO AS A FUNCTION OF 11 AND m amznm. Avnzun INVENTOR.

fieissuea Au 12, 1915 Re. 28,511

I I I 25 Sheets-Sheet 17 THICKNESS RATIO WPOSS'BLE IMPOSSIBLE EQ.(I2) 2.0!

THICKNESS RATIO ,HNUHHHIHHHHW v I lrrIfI/IIIIIIII! SEMI-CONE ANGLE FIG.I| THICKNESS RATIO AS A FUNCTION OF a BETZALEL A'ITITZUR IN VENTOR.

Reissued Aug. 12, 1975 25 Sheets-Sheet 19 2O WALL TENSION 4141.41.41.44 ELlMlNATED SEMI-CONE ANGLE MANDREL FRICTION F|G.|3 CRITICAL SEMI-CONE ANGLE OF THE DIE TO PREVENT WALL TENSION.

BE'IZALEL AVITZUR INVENTOR. 

1. In a method of shaping a hollow workpiece with the aid of a punch and a die having an aperture extending therethrough, said aperture including a conical portion having a semi-cone angle Alpha ; the steps of providing said workpiece with a side wall having an inner and an outer surface; causing said punch to engage said inner surface of the side wall of the hollow workpiece so that the latter is positioned on said punch; moving said punch with said workpiece thereon relative to said die and into said conical portion of the aperture thereof to iron said side wall and thereby reduce the thickness and increase the length thereof to a predetermined degree while subjecting said workpiece to differential frictional forces including a predetermined, relatively large frictional force resulting from contact of said inner surface of the side wall with said punch, and a smaller frictional force acting on said outer surface of the side wall and resulting from movement of said side wall relative to said die, said differential frictional forces being effective to limit tensile stresses in the ironed portion of said side wall during ironing; and controlling said differential frictional forces in part by said semi-cone angle Alpha being (in agreement with the equation
 2. A method as defined in claim 1, wherein said die has a single ironing portion, and said workpiece is ironed to a predetermined final degree during passage through said single ironing portion.
 3. A method as defined in claim 1, including the step of providing said punch with a surface rougher than the inner surface of said tapered aperture of the die, the relatively rough surface of said punch being caused to engage said interior surface of the side wall of the workpiece.
 4. A method as defined in claim 1, in which said aperture of the die includes a substantially cylindrical portion, and the magnitude of said relatively large frictional force is in accordance with the expression
 5. A method as defined in claim 4, wherein the ironed portion of said side wall is kept substantially free of tensile stresses during the ironing step and, accordingly, said expression is reduced to
 6. A method as defined in claim 5, wherein said semi-cone angle Alpha of the conical portion of the die aperture is smaller than approximately 55* and thus the reduced expression is approximately equal to
 7. A method as defined in claim 4, wherein the portion of said side wall emerging from said conical portion of the die aperture is subjected to tensile stresses in accordance with the equation
 8. A method as defined in claim 4, in which the thickness of said side wall is reduced in accordance with the equation
 9. A method as defined in claim 8, in which the ironed portion of said side wall is kept substantially free of tensile stresses during the ironing step and, accordingly, the last-cited equation is reduced and modified to
 10. In a method of shaping a hollow workpiece with the aid of a punch and a die having an aperture extending therethrough, said aperture including a conical portion and a substantially cylindrical portion; the steps of providing said workpiece with a side wall having an inner and an outer surface; causing said punch to engage said inner surface of the side wall of the hollow workpiece so that the latter is positioned on said punch; moving said punch with said workpiece thereon relative to said die and into said conical portion of the aperture thereof to iron said side wall and thereby reduce the thickness and increase the length thereof to a predetermined degree while subjecting said workpiece to differential frictional forces including a predetermined, relatively large frictional force resulting from contact of said inner surface of the side wall with said punch, and a smaller frictional force acting on said outer surface of the side wall and resulting from movement of said side wall relative to said die, said differential frictional forces being effective to limit tensile stresses in the ironed portion of said side wall during ironing; and controlling said smaller frictional force by providing hydrodynamic lubrication in the area in which said outer surface of the side wall of the workpiece passes through said aperture of the die, said hydrodynamic lubrication being obtained under conditions represented by the equation
 11. A method as defined in claim 10, in which with friction at the die being negligible the portion of said side wall emerging from said conical portion of the die aperture is subjected to tensile stresses in accordance with the equation
 12. In a method of shaping a cup-like workpiece from a substantially flat blank with the aid of a punch and die means having an aperture extending therethrough, said aperture including a conical portion having a semi-cone angle Alpha ; the steps of causing said blank to abut said die means; advancing said punch relative to said die means so as to draw said blank into said aperture and impart thereto the form of a cup having a side wall and a bottom integral therewith, said side wall having an outer and an inner surface; continuing the movement of said punch relative to said die means to introduce said workpiece into said conical portion of the aperture of the die means and iron said side wall and thereby reduce the thickness and increase the length thereof to a predetermined degree while subjecting said workpiece to differential frictional forces including a predetermined, relatively large frictional force resulting from contact of said inner surface of the side wall with said punch, and a smaller frictional force acting on said outer surface of the side wall and resulting from movement of said side wall relative to said die means, said differential frictional forces being effective to minimize application of forces to said bottom of the cup-shaped workpiece and thereby limit tensile stresses in the ironed portion of said side wall during ironing; and controlling said differential frictional forces in part by said semi-cone angle Alpha being (in agreement with the equation
 13. A method as defined in claim 12, including the steps of starting said ironing substantially immediately after formation of said bottom while keeping the ironed portion of said workpiece generally free of tensile stresses during ironing.
 14. In apparatus for shaping a hollow workpiece provided with a side wall having an inner and an outer surface; die means having an aperture extending therethrough, said aperture including a conicAl ironing portion; a punch movable relative to said die means and arranged to engage said inner surface of the side wall of the workpiece for advancing the latter into said ironing portion of the die aperture so as to iron said workpiece; first means for subjecting said workpiece to a predetermined, relatively large frictional force resulting from contact of said inner surface of the side wall with said punch; and second means for subjecting said workpiece to a smaller frictional force acting on said outer surface of the side wall and resulting from movement of said side wall relative to said die means; said first and second means being effective to limit tensile stresses in said side wall during ironing; and said conical portion of the aperture of the die means having a semi-cone angle Alpha (in accordance with the equation
 15. Apparatus as defined in claim 14, wherein said first means includes a punch surface rougher than the surface of said aperture of the die means, said rougher surface of the punch being arranged to engage said inner surface of the side wall of the workpiece.
 16. Apparatus as defined in claim 15, wherein said second means includes an actuating device for moving said punch and workpiece relative to said die means at a rate sufficient for hydrodynamic lubrication of the area in which said outer surface of the side wall of the workpiece passes through said ironing portion of the die aperture.
 17. Apparatus as defined in claim 14, wherein said aperture of the die means includes a drawing portion preceding said ironing portion and cooperating with said punch for drawing said workpiece from a substantially flat blank to the shape of a cup and for thereby producing said side wall and a bottom integral therewith prior to and in series with the ironing operation; and wherein said drawing and ironing portions of the aperture of the die means are arranged so close to each other that ironing will commence as soon as said bottom of the workpiece emerges from said drawing portion of the aperture of the die means.
 18. Apparatus as defined in claim 17, wherein said drawing portion merges into said ironing portion. 